A standard bulk-storage apparatus has a large hopper adapted to hold a large supply of bulk material and having a floor formed with a central outlet opening centered on a vertical axis and a side wall extending upward from the floor. An upwardly tapered hood generally centered on the axis and open downwardly toward the opening has a lower edge vertically spaced from the floor around the opening. A drive supported in the hood has a rotary output projecting down into the space between the floor and the lower edge above the opening and carries an arm sweepable over the floor around the opening by the drive.
Thus, as the drive orbits the arm, bulk material is swept into the central opening, to fall down through an outlet tube to an appropriate horizonal conveyor or the like. Such an arrangement can be used with coal, grain, ore, or the like, and is typically employed with dusty materials. It is not uncommon for such arrangements to be very large, with a rotor some 3 m in diameter.
The drive must, of course, be serviced periodically. As a rule this is done when the hopper is empty, so cover plates in the sides of the uncovered hood can be removed to gain access to the drive in its interior. Obviously this exposes the worker to whatever dust or the like is left over from the material that hitherto filled the hopper. In addition it requires that the hopper be run empty, which is not advisable in many systems and production operations.
A system breakdown is much more serious. To make repairs the hopper must be emptied to allow the service people to gain access to the drive. This can be an extremely onerous job requiring shoveling or vacuuming the material out of the hopper. Days of down time can be wasted just emptying out the hopper so the necessary repairs can be made. This is particularly irksome when only the repair needed is a relatively minor one.